1. Field of the Invention
The field of the invention is tunnel boring machines. More specifically, the present invention relates to a tunnel boring machine having an articulated excavator and a breast plate assembly.
2. Description of the Prior Art
Heretofore various types of tunnel boring machines have been proposed for digging a tunnel through material of intermediately hardness and containing loose earth and rock. Such tunnel boring machines typically include a heavy style hollow cylindrical body having a front circular cutting edge and a central axis. An excavator is mounted at the front end of the machine within the cylinder and generally on the central axis of the machine. A conveyor is mounted within the cylindrical body with a loading end thereof situated adjacent the bottom portion of the circular cutting edge. The excavator is operable to cut through material at the front of the machine and move it onto the conveyor.
At the back of the machine mechanisms are provided for positioning quarter-cylindrical precast concrete segments in a circular ring behind the cylindrical body to form an increment of tunnel liner behind the machine.
In the tunnel behind the tunnel boring machine there is mounted a track on which flat cars containing concrete segments can travel to bring segments to the tunnel boring machine and on which gondola cars can travel to the machine for receiving material from the conveyor and carrying the material out of the tunnel.
In digging a tunnel, the tunnel boring machine is positioned at the front of the beginning portion of a tunnel liner. Retractable jack assemblies each including a plurality of jacks are located at the read edge of the cylindrical body and positioned between the rear edge and the front edge of the tunnel liner being formed. The jacks are then extended in increments to force the front circular cutting edge against the material being excavated.
Also, the excavator is operated to remove the material at the front end of the cylindrical body. After an amount of material has been dug out by the excavator and placed on the conveyor, the jacks are extended to push the cutting edge against the material at the outer periphery of the hold being dug by the excavator to finish the cut of the hold to form the tunnel. After the jacks have been extended a predetermined distance, at least equal to the width of the precast quarter-cylindrical segments, the jacks are contracted and the jack assemblies are retracted. Then four concrete segments are positioned in a ring in the space vacated by the retracted jack assemblies the cylindrical body and against the front edge of the tunnel liner.
Next, the jack assemblies are positioned in the space between the new front edge of the liner formed by the four concrete segments just laid in place and the excavator is operated again to dig a hole in the material at the front of the tunnel boring machine. The jacks are periodically extended to push the cylindrical body member toward the hole being dug and to finish the cut of the hole at the outer periphery thereof.
The procedure described above is repeated over and over again until the tunnel is completed.
To prevent material from falling into the front end of the tunnel boring machine as the excavator is digging out the material at the front of the machine, a plurality of breast plates are provided hingedly connected to the inner periphery of the cylindrical body. Typically, such breast plates are arranged in an assembly to form a partially annular shield beneath the top portion of the circular cutting edge of the cylindrical body and above the excavator. Piston and cylinder assemblies are associated with the breast plates for pivoting the breast plates upwardly to hold material from falling into the machine.
Heretofore the excavators often included a bucket-boom assembly comprising a bucket-scoop pivotally mounted at the front end of a boom which is mounted to a bulkhead that can be reciprocated along the central axis of the machine. The boom is rotatable 360.degree. about the central axis and is pivotally mounted to the bulkhead. The assembly includes two reciprocal power mechanisms, one for pivoting the boom about the central axis and another for pivoting the bucket-scoop about the outer end of the boom. In this way four degrees of movement of the excavator are provided which are as follows: (1) reciprocal movement of the boom along the central axis of the cylindrical body; (2) rotation of the boom about the central axis (3) pivoting movement of the boom to move the outer end thereof toward and away from the central axis and; (4) pivotal movement of the bucket-scoop about the outer end of the boom.
With this type of excavator, a large breakout force is obtained at the center of the hole in the material being dug out by the bucket-boom assembly. However, only about half of that breakout force is obtained at the periphery of the hole being dug.
As will be explained in greater detail hereinafter, the articulated boom-dipper-bucket assembly of the present invention provides an excavator which has five degrees of movement with the addition of a dipper member to the assembly. With five degrees of motion, a more uniform breakout force is obtained across the radial extent of movement of the bucket-scoop of the excavator from the central axis of the machine to the circular cutting edge of the machine.